Pulsed ablating thruster apparatus



June 3, 1969 F. N. MAs-rRuP 3,447,322

I PULSED ABLATING THRUSTER APPARATUS i Filed oct. 25, 196e sheet af 2 Vo a e D. C. SOUICB `\52 Frthjof N. Most INVENTO June 3, 1969 F. N. MAsTRuP PULSED ABLATING THRUSTER APPARATUS Sheet 2 of2 Filed Oct. 25, 1966 Fig. 3.

Frithjof N. Mastrup,

I NVENTOR.

AGENT.

United States Patent O PULSED ABLATING Tl-lRUSTER APPARATUS Frithjof N. Mastrup', Manhattan Beach., Calif., asslgnor to TRW Inc., vRedondo Beach, Calif., a lcorporation of Ohio Filed Oct. 25, 1966, Ser. No. 589,348 Int. Cl. F02k 11/00; H01j I /02; H05b 7/02 U.S. Cl. 60-203 5 Claims ABSTRACT OF THE DISCLOSURE Propulsion apparatus having a body with a passage therethrough, the body being of dielectric material capable of releasing gas when subjected to heat. One electrode member is positioned to seal one end of the passage and another electrode member with an aperture therein is positioned in the other end of the passage. Electrical apparatus is connected to the electrode to generate electrical discharge arcs along the passage to effect heating of the material to release gas therefrom intoy the passage and through the passage and out the other electrode member to develop thrust in the body.

This invention relates generally to rocket propulsion apparatus, andY more particularly relates to pulsed mode thruster apparatus producing thrust in a member by means of plasma ablated from the member.

Briefly, in accordance with the invention there is provided novel propulsion apparatus capable of use in high vacuum conditions such as encountered in space environments wherein stored electrical energy is'discharged in an arc confined to a chamber in the interior of a dielectric insulating material body. The arc is initiated by a sliding spark and is sustained by the dielectric material ablated from the walls of the chamber to form plasma at high pressure. The "plasma escapes at one end of the chamber through one electrode which has a passage therethrough and is shaped in the form of a rocket nozzle. The other electrode blocks the other end of the chamber to compel the plasma to exit only through the nozzle to provide thrust to the body.

In the drawings:

FIG. 1 is a perspective pictorial showing of the novel propulsion ap'paratus of the invention;

FIG. 2 is a iside elevation view in section-of the thruster and a schematic diagram of the electrical circuit of the propulsion apparatus of FIG. 1; and

FIG. 3 is a graph depicting the average momentum irnpulse versus the energy dissipated in the thruster of FIGS. 1 and 2 constructed in accordance with this invention.

Referring now to FIG. 1 the novel propulsion apparatus of the present invention is shown as consisting of an ablating thruster body 10, an expansion nozzle 12 connected to one end of the thruster body, an 'electrode 14 connected to the other end of the thruster body, an electrical line 16 connecting an electrical power supply circuit 18 to the electrode 14, and an electrical line 20 connecting the nozzle 12 to the circuit 18.

Referring now to FIG. 2, the thruster body is shown as an elongated cylindrical shaped member fashioned from dielectric plastic material. It has been found that materials such as Plexiglas, nylon, and Teflon are suitable materials for the member 10. It should be understood that there is a wide variety of materials which are suitable for use to fashion the member and that the present invention is not limited to those specific preferred materials mentioned above.

A cylindrical bore 22 having a wall 23 is provided within the thruster body 10 to serve as a spark discharge channel. At one end the bore is slightly enlarged and pro- 3,447,322 Patented June 3, 1969 ice vided with threads 24. The other end of the bore 22 is also enlarged and threaded at 26.

Expansion nozzle 12 is preferably fashioned from electrical conducting metal such as stainless steel or the like with a throat portion 27, suitably threaded at" 28 to engage the' threads 24, and an expansion porti-on 30. A threaded bore 32 in the expansion portion 30 `is adapted to receive a suitable threaded connection (not shown) which is adapted to be connected to the electrical line 20.

The metallic electrode 14 is shown as havinga portion 34 adapted to closely t the bore 22 and external threads 36 engageable with the internal threads 26. T lie portion 34 is bored at 38 and counterbored at 40. A threaded bore 42 in the electrode 14 is adapted to receive a suitable connector (not shown) which is adapted for connection to the line 16.

The electrical power supply circuit 18 consists of a switch 44 connected to the line 16 and a parallel arrangement of a capacitor 50 and a high voltage D.C. source S2 with a series charging resistor 53. The line 20 is connected to the capacitor 50 and voltage source 52. The switch 44 can be a conventional ignitron switch or the like capable of providing variable switch rates. The direct current source 52 should be capable of supplying D.C. potentials of up to about 5 kv.

In operation the capacitor S0 is initially charged to a voltage V0 with resultant stored energy in the capacitor according to the equation 1/2CV02, where C is the capacitance of the capacitor 50. When the switch is closed, the voltage V0 of the capacitor 50 is suddenly applied to the electrodes 12 and 14 across the bore 22. If a sufliciently high voltage V0 is applied a sliding high vacuum spark rst develops on the bore wall 23 and vaporizes a small amount of the dielectric material of body 10 to form gaseous products which discharge into the bore 22. The gaseous products thus discharged into the bore 22 serve as the carrier gas or plasma for the electrical discharge arc which now develops. Upon initiation of the electrical discharge arc heat transfer to the wall 23 of the bore 22 evolves yet more gaseous products to build up pressure in the bore on'the order of one to a hundred atmospheres and at a temperature of about 251,000 K. The gas products escape from the bore 22 tlrugh the nozzle 12 thereby imparting thrust to the apparatus including the member 10. The escapinglgaseous products also radiate energy in the ultraviolet;visible, and infrared region of the spectrum. If now the switch 44 is opened to allow the capacitor to charge to the voltage V0 and again closed to discharge the capacitor, a repetition of the cycle of events hereinbeforefset forth results, thus providing pulsed mode thrust generation. Average thrust output can be controlled simply by varying the electrical energy 1/2CV02 applied to the capacitor 50. This can be accomplished by varying the applied voltage V0 generated by the voltage source 52. Thrust output can also be controlled by varying the discharge rate of capacitor 50. This can be accomplished by regulating the rate at which the switch 44 is opened and closed.

Referring to FIG. 3, wherein test data obtained on thruster apparatus constructed in accordance with this invention is exemplified by the curve 54, it can be seen Ifrom inspection of curve 54 that impulse versus the electrical energy dissipated in the thruster body is approximately a linear function.

The advantages of the thruster apparatus of the present invention are numerous and is especially adapted for operation in the high vacuum conditions encountered in space. Neither gas, liquids, nor chemically reactive substances have to be supplied to the thruster body. Fuel injection systems are not needed. The thruster Ibody is 3 compact and has no moving parts and is very resistant to damage by impact and vibration.

While I have described and illustrated a specic embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be made without departing from the true spirit and scope of the invention as dened in the appended claims.

What I vclaim is:

1. In combination, comprising:

a -body member having a passage therethrough, said body member being of dielectric material capable of releasing gas when subjected to heat;

a pair of electrodes, one of said electrodes sealing one end of said passage and the other of said electrodes having an aperture opening the other end of said passage; and

means for applying electrical potential between said electrodes to generate electrical discharge arcs along said passage to effect heating of said material to a .predetermined temperature to release gas therefrom into said passage at a predetermined pressure and through said passage and aperture to develop thrust in said body member.

2. The combination as set forth in claim 1, wherein the other of said electrodes is a gas expansion nozzle.

3. The combination as set forth in claim 1 said electrical potential applying means comprising:

an electrical circuit arrangement consisting of electric charge storage means as a D C. potential source; and

switch means for periodically connecting said circuit arrangement across said pair of electrodes to discharge said charge storage means.

4. The combination as set forth in claim 1, wherein said temperature is on the order of 20,000 K. and the pressure is greater than one atmosphere but less than two hundred atmospheres.

5. In combination, comprising:

a body member having a passage therethrough, said body member being of dielectric material capable of releasing gas radiating radiant energy into said passage When subjected to the heating of electrical discharge arcs developed within said passage;

a rst electrode sealing one end of said passage;

a second electrode in the form of a gas expansion nozzle positioned in said passage to open the other end of said passage;

a parallel electric circuit arrangement consisting of capacitor means and a D.C. potential source; and switch means for periodically connecting said circuit arrangement across said electrodes to discharge said capacitor means to generate said electrical discharge arcs along said passage to eiect heating of said material to a temperature of about 20,000 K. to release said -gas therefrom into said passage at a pressure on the order of more than one atmosphere but less than two hundred atmospheres and through said passage and gas expansion nozzle to develop thrust in said body member.

References Cited UNITED STATES PATENTS 2,765,975 10/ 1956 Lindenblad 60-203 XR 2,816,419 12/1957 Mueller 60-39.48 3,140,421 7/1964 Spongberg 219-121 XR 3,156,092 11/1964 Holzman 60-251 3,358,452 12/1967 Ehrenfeld et al. 60,-200

CARLTON R. COYLE, Primary Examiner.

U.S. C1. XR. 

